Conceptually, complex systems appear in disciplines from biology [1]}, [2]} to physics [3]} to sociology [4]}, [5]}. The interdisciplinary field of complex systems grew out of these and several other disciplines in the latter half of the twentieth century with a few core methods for understanding adaptation, information, and collective behaviors [6]}. Newman [7]} notes that “there is no precise technical definition of a `complex system,' but that most researchers in the field would probably agree that it is a system composed of many interacting parts, such that the collective behavior of those parts together is more than the sum of their individual behaviors.” An important characteristic of complex systems is what are called emergent behaviors, the unexpected macroscopic behaviors that often result from simple microscopic interactions between constituent elements [6]}, [7]}. These characteristics—significant interactions and emergent behaviors—collectively suffice to begin defining engineered versions of such systems.The term complexity also appears throughout the complex systems literature, along with the field of complexity science. For the purposes of this article, complexity refers to the characteristics of a complex system and are thus roughly synonymous with complex systems, though entire texts exist to define the term and field more completely [6]}.
